WASHINGTON (AP) - The spending scandal at the General Services Administration could just be the tip of the iceberg.

According to the agency's inspector general, he's investigating other potential wrongdoing -- including possible bribery and kickbacks. Brian Miller told a House panel that "all sorts of improprieties" are being looked into.

At today's hearing, lawmakers hoped to hear from Jeffrey Neely -- the GSA official who was largely responsible for a Las Vegas conference of GSA employees that cost $823,000. But he invoked his right to remain silent.

Neely could face a criminal investigation by the Justice Department. He's been placed on leave as a regional executive in Western states for the agency that is in charge of federal buildings and supplies.

Martha Johnson, who resigned as chief of the agency after the report about the Las Vegas conference, told the panel that the conference became a "raucous, extravagant, arrogant, self-congratulatory event." She apologized to the American people for it.

Lawmakers accused her of sitting on the findings for 11 months after she received an interim briefing from the inspector general.